1. Field of the Invention
The invention relates in general to the monitoring of refrigerated containers over electrical distribution power lines, and more specifically to the mapping of container addresses in such a monitoring system.
2. Description of the Prior Art
Concurrently filed Application Ser. No. 189,566 entitled "Power Line Carrier Communication System For Monitoring Refrigerated Containers" describes an arrangement for monitoring refrigerated containers, called "reefers", aboard ships and in ship terminals. The above mentioned application is hereby incorporated into the specification of the present application by reference. In general, the described power line carrier monitoring system monitors the temperatures and other status signals of the reefers by utilizing a master monitoring unit (MMU) which applies polling commands to an electrical distribution power line via a network central control unit (NCCU). Remote monitoring units (RMUs) associated with the reefers to be monitored pick up polling commands from the electrical distribution power line, and they prepare and return status messages to the MMU via the power line and the NCCU when each is uniquely addressed by the MMU.
One of the functions of the MMU is to log-in or map the connections of the reefers to be monitored as they are connected to the electrical distribution power line. Simply requesting any newly connected reefer to return its address to the MMU when initially connected is not practical, as there may be several hundred reefers. Upon powerup or system initialization all would try to use the power line at once. Error checking schemes in the messages would indicate the collisions, and the MMU would discard any address received in error. Thus, a method of orderly logging the unique addresses of the reefers into the MMU is required, so the MMU will thereafter periodically monitor all reefers connected to the monitoring system.